/*
 * $Id: GaussianBlurFilter.java 4082 2011-11-15 18:39:43Z kschaefe $
 *
 * Dual-licensed under LGPL (Sun and Romain Guy) and BSD (Romain Guy).
 *
 * Copyright 2006 Sun Microsystems, Inc., 4150 Network Circle,
 * Santa Clara, California 95054, U.S.A. All rights reserved.
 *
 * Copyright (c) 2006 Romain Guy <romain.guy@mac.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.jdesktop.swingx.image;

import java.awt.image.BufferedImage;

import org.jdesktop.swingx.util.GraphicsUtilities;

public class GaussianBlurFilter extends AbstractFilter {
	private final int radius;

	/**
	 * <p>
	 * Creates a new blur filter with a default radius of 3.
	 * </p>
	 */
	public GaussianBlurFilter() {
		this(3);
	}

	/**
	 * <p>
	 * Creates a new blur filter with the specified radius. If the radius is
	 * lower than 0, a radius of 0.1 will be used automatically.
	 * </p>
	 *
	 * @param radius
	 *            the radius, in pixels, of the blur
	 */
	public GaussianBlurFilter(int radius) {
		if (radius < 1) {
			radius = 1;
		}

		this.radius = radius;
	}

	/**
	 * <p>
	 * Returns the radius used by this filter, in pixels.
	 * </p>
	 *
	 * @return the radius of the blur
	 */
	public int getRadius() {
		return radius;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public BufferedImage filter(BufferedImage src, BufferedImage dst) {
		int width = src.getWidth();
		int height = src.getHeight();

		if (dst == null) {
			dst = createCompatibleDestImage(src, null);
		}

		int[] srcPixels = new int[width * height];
		int[] dstPixels = new int[width * height];

		float[] kernel = createGaussianKernel(radius);

		GraphicsUtilities.getPixels(src, 0, 0, width, height, srcPixels);
		// horizontal pass
		blur(srcPixels, dstPixels, width, height, kernel, radius);
		// vertical pass
		blur(dstPixels, srcPixels, height, width, kernel, radius);
		// the result is now stored in srcPixels due to the 2nd pass
		GraphicsUtilities.setPixels(dst, 0, 0, width, height, srcPixels);

		return dst;
	}

	/**
	 * <p>
	 * Blurs the source pixels into the destination pixels. The force of the
	 * blur is specified by the radius which must be greater than 0.
	 * </p>
	 * <p>
	 * The source and destination pixels arrays are expected to be in the
	 * INT_ARGB format.
	 * </p>
	 * <p>
	 * After this method is executed, dstPixels contains a transposed and
	 * filtered copy of srcPixels.
	 * </p>
	 *
	 * @param srcPixels
	 *            the source pixels
	 * @param dstPixels
	 *            the destination pixels
	 * @param width
	 *            the width of the source picture
	 * @param height
	 *            the height of the source picture
	 * @param kernel
	 *            the kernel of the blur effect
	 * @param radius
	 *            the radius of the blur effect
	 */
	static void blur(int[] srcPixels, int[] dstPixels, int width, int height, float[] kernel, int radius) {
		float a;
		float r;
		float g;
		float b;

		int ca;
		int cr;
		int cg;
		int cb;

		for (int y = 0; y < height; y++) {
			int index = y;
			int offset = y * width;

			for (int x = 0; x < width; x++) {
				a = r = g = b = 0.0f;

				for (int i = -radius; i <= radius; i++) {
					int subOffset = x + i;
					if (subOffset < 0 || subOffset >= width) {
						subOffset = (x + width) % width;
					}

					int pixel = srcPixels[offset + subOffset];
					float blurFactor = kernel[radius + i];

					a += blurFactor * ((pixel >> 24) & 0xFF);
					r += blurFactor * ((pixel >> 16) & 0xFF);
					g += blurFactor * ((pixel >> 8) & 0xFF);
					b += blurFactor * ((pixel) & 0xFF);
				}

				ca = (int) (a + 0.5f);
				cr = (int) (r + 0.5f);
				cg = (int) (g + 0.5f);
				cb = (int) (b + 0.5f);

				dstPixels[index] = ((ca > 255 ? 255 : ca) << 24) | ((cr > 255 ? 255 : cr) << 16) | ((cg > 255 ? 255 : cg) << 8)
						| (cb > 255 ? 255 : cb);
				index += height;
			}
		}
	}

	static float[] createGaussianKernel(int radius) {
		if (radius < 1) {
			throw new IllegalArgumentException("Radius must be >= 1");
		}

		float[] data = new float[radius * 2 + 1];

		float sigma = radius / 3.0f;
		float twoSigmaSquare = 2.0f * sigma * sigma;
		float sigmaRoot = (float) Math.sqrt(twoSigmaSquare * Math.PI);
		float total = 0.0f;

		for (int i = -radius; i <= radius; i++) {
			float distance = i * i;
			int index = i + radius;
			data[index] = (float) Math.exp(-distance / twoSigmaSquare) / sigmaRoot;
			total += data[index];
		}

		for (int i = 0; i < data.length; i++) {
			data[i] /= total;
		}

		return data;
	}
}
